. Cosmology II: The thermal history of the Universe . Ruth Durrer Département de Physique Théorique et CAP Université de Genève Suisse August 6, 2014 . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 1 / 21
Contents . . The thermal history of the Universe 1 . . The cosmic microwave background 2 . . Dark matter 3 . . Dark energy models 4 . . Conclusions 5 . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 2 / 21
Thermal history In the past the Universe was not only much denser than today but also much hotter. The most remarkable events of the hot Universe: Recombination (electrons and protons combine to neutral hydrogen). Age of the Universe: t 0 ≃ 13 . 7 billion years . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 3 / 21
Thermal history In the past the Universe was not only much denser than today but also much hotter. The most remarkable events of the hot Universe: Recombination (electrons and protons combine to neutral hydrogen). Nucleosyhthesis (the formation of Helium, Deuterium, ...) Age of the Universe: t 0 ≃ 13 . 7 billion years . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 3 / 21
Thermal history In the past the Universe was not only much denser than today but also much hotter. The most remarkable events of the hot Universe: Recombination (electrons and protons combine to neutral hydrogen). Nucleosyhthesis (the formation of Helium, Deuterium, ...) Inflation ? Age of the Universe: t 0 ≃ 13 . 7 billion years . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 3 / 21
Recombination Since the photon (radiation) energy density scales like T 4 ∝ R − 4 ∝ ( z + 1 ) 4 while the matter density scales like mn ∝ R − 3 ∝ ( z + 1 ) 3 , at very early time, the ∼ 10 4 years). Universe is radiation dominated ( z > ∼ 4000, t < . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 4 / 21
Recombination Since the photon (radiation) energy density scales like T 4 ∝ R − 4 ∝ ( z + 1 ) 4 while the matter density scales like mn ∝ R − 3 ∝ ( z + 1 ) 3 , at very early time, the ∼ 10 4 years). Universe is radiation dominated ( z > ∼ 4000, t < At T ≃ 3000K ( t ≃ 300 ′ 000years) the Universe is ’cold’ enough that protons and electrons can combine to neutral hydrogen. . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 4 / 21
Recombination Since the photon (radiation) energy density scales like T 4 ∝ R − 4 ∝ ( z + 1 ) 4 while the matter density scales like mn ∝ R − 3 ∝ ( z + 1 ) 3 , at very early time, the ∼ 10 4 years). Universe is radiation dominated ( z > ∼ 4000, t < At T ≃ 3000K ( t ≃ 300 ′ 000years) the Universe is ’cold’ enough that protons and electrons can combine to neutral hydrogen. After this, photons no longer scatter with matter but propagate freely. Their energy (and hence the temperature) is redshifted to T 0 = 2 . 728K today, corresponding to a density of about 400 photons per cm 3 . . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 4 / 21
Recombination Since the photon (radiation) energy density scales like T 4 ∝ R − 4 ∝ ( z + 1 ) 4 while the matter density scales like mn ∝ R − 3 ∝ ( z + 1 ) 3 , at very early time, the ∼ 10 4 years). Universe is radiation dominated ( z > ∼ 4000, t < At T ≃ 3000K ( t ≃ 300 ′ 000years) the Universe is ’cold’ enough that protons and electrons can combine to neutral hydrogen. After this, photons no longer scatter with matter but propagate freely. Their energy (and hence the temperature) is redshifted to T 0 = 2 . 728K today, corresponding to a density of about 400 photons per cm 3 . This cosmic microwave background can be observed today in the (1– 400)GHz range. It has a perfect blackbody spectrum. . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 4 / 21
Recombination Since the photon (radiation) energy density scales like T 4 ∝ R − 4 ∝ ( z + 1 ) 4 while the matter density scales like mn ∝ R − 3 ∝ ( z + 1 ) 3 , at very early time, the ∼ 10 4 years). Universe is radiation dominated ( z > ∼ 4000, t < At T ≃ 3000K ( t ≃ 300 ′ 000years) the Universe is ’cold’ enough that protons and electrons can combine to neutral hydrogen. After this, photons no longer scatter with matter but propagate freely. Their energy (and hence the temperature) is redshifted to T 0 = 2 . 728K today, corresponding to a density of about 400 photons per cm 3 . This cosmic microwave background can be observed today in the (1– 400)GHz range. It has a perfect blackbody spectrum. It represents a ’photo’ of the Universe when it was about 300’000 years old, corresponding to a redshift of z ≃ 1100. . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 4 / 21
The cosmic microwave background: the spectrum (Fixen et al. 1996) Nobel Prize 1978 for Penzias and Wilson, Nobel Prize 2006 for Mather T 0 = 2 . 728K ≃ − 270 . 5 o C . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 5 / 21
The cosmic microwave background: anisotropies Map of the CMB temperature: per- fectly isotropic. Subtracting the monopole a dipole of amplitude ∼ 10 − 3 becomes vis- ible. It is mainly due to the motion of the solar system with respect of the sphere of emission (last scatter- ing surface). And what is this? Left over after subtracting the dipole. Fluctuations of amplitude ∼ 10 − 5 . Smoot et al. (1999), Nobel Prize 2006 . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 6 / 21
The cosmic microwave background: anisotropies ESA/Planck (2013) . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 7 / 21
The cosmic microwave background: anisotropies Angular scale 90 � 18 � 1 � 0.2 � 0.1 � 0.07 � 6000 5000 4000 D � [ µ K 2 ] 3000 2000 1000 0 2 10 50 500 1000 1500 2000 2500 Multipole moment, � ESA/Planck (2013) ℓ = 200 corresponds to about 1 o . ⇒ ’acoustic’ peaks. ( θ ≃ 180 o /ℓ ) (This is roughly the double of the angular size of the full moon (or of the sun).) . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 8 / 21
The cosmic microwave background: anisotropies The matter distribution in the observed Universe is not very homogeneous and isotropic. It is in form of galaxies, clusters, filaments, voids. The idea is that these large scale structures formed by gravitational instability from small initial fluctua- tions which have been set up during inflation. . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 9 / 21
The cosmic microwave background: anisotropies The matter distribution in the observed Universe is not very homogeneous and isotropic. It is in form of galaxies, clusters, filaments, voids. The idea is that these large scale structures formed by gravitational instability from small initial fluctua- tions which have been set up during inflation. These initial fluctuations are also imprinted in the CMB. . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 9 / 21
The cosmic microwave background: anisotropies The matter distribution in the observed Universe is not very homogeneous and isotropic. It is in form of galaxies, clusters, filaments, voids. The idea is that these large scale structures formed by gravitational instability from small initial fluctua- tions which have been set up during inflation. These initial fluctuations are also imprinted in the CMB. Once a given scale enters the horizon, fluctuations on this scale begin to oscillate like acoustic waves (sound). The first peak corresponds to fluctuations which have had time to make exactly 1 contraction since horizon entry until decoupling. . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 9 / 21
The cosmic microwave background: anisotropies The matter distribution in the observed Universe is not very homogeneous and isotropic. It is in form of galaxies, clusters, filaments, voids. The idea is that these large scale structures formed by gravitational instability from small initial fluctua- tions which have been set up during inflation. These initial fluctuations are also imprinted in the CMB. Once a given scale enters the horizon, fluctuations on this scale begin to oscillate like acoustic waves (sound). The first peak corresponds to fluctuations which have had time to make exactly 1 contraction since horizon entry until decoupling. The second peak peak corresponds to fluctuations which have had time to make exactly 1 contraction and 1 expansion since horizon entry until decoupling (under density). . . . . . . Ruth Durrer (Université de Genève) Cosmology II August 6, 2014 9 / 21
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